Process for preparing blown vegetable oil

ABSTRACT

A method for partially refining a crude vegetable oil utilizing physical refining techniques is described. The crude vegetable oil is first degummed by either (1) allowing the crude oil to settle over a period of time, such as twenty days, so that the oil becomes stratified into at least two layers, wherein one layer comprises gums with low oil content and a second layer comprises oil containing only a fraction of the gums originally present and then separating the oil layer from the gum layer, or (2) heating the crude oil to a temperature of about 270-300° F. with agitation and then allowing the crude oil to settle for a period of time until the oil becomes stratified into the at least two layers. The degummed oil is then aerated and agitated while being maintained at a temperature of 170-180° F. for a time period sufficient to obtain a desired oil viscosity. The resulting partially refined oil is suitable for use in industrial applications such as the preparation of urethane foams.

CROSS-REFERENCE TO RELATED APPLICATIONS Not Applicable. STATEMENTREGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not Applicable.BACKGROUND OF THE INVENTION

[0001] The present invention relates to the refining of crude vegetableoils, and in particular the refining of crude soybean oil, to render theoil useful in industrial applications.

[0002] Refined vegetable oils and compounds and materials derivedtherefrom have a number of uses in industrial applications. For example,refined soy oil can be used as an ecological alternative to productsderived from petroleum that are used in making urethane foams. Onedifficulty with using such refined vegetable oils, however, is that thecosts associated with the refining process make the refined vegetableoils to expensive to use in industrial applications.

[0003] Crude oil that has been extracted from the oil-containingvegetable material is typically a dark colored turbid liquid that needsto be further refined to convert it to a useful oil product. There are awide variety of known techniques for refining crude vegetable oils intouseful vegetable oils. Because most of the refined vegetable oils areintended for human consumption, most of the conventional methods andequipment used in vegetable oil processing are directed to removingimpurities that can contribute to unwanted flavor, color, odor, andother undesirable properties. Such impurities includephosphorus-containing contaminants such as hydratable and non-hydratablephospholipids, free fatty acids, color bodies and trace minerals. Thetypical known vegetable oil refining process involves several steps,such as degumming, neutralization (alkali refining), bleaching anddeodorization. The degumming step typically involves adding water andusually other chemicals, such as phosphoric acid, to the crude oil,heating and agitating the mixture for a period of time (approximately10-30 minutes) at temperatures of about 50-70° C., and then subsequentlycentrifuging the mixture to separate the water and oil. The degummingstep can be repeated to further reduce the amount of phospholipids inthe crude oil.

[0004] The degummed oil is then subjected to several additional refiningsteps to remove the other unwanted components such as free fatty acids,color bodies, and other impurities. In these refining steps, the freefatty acids are saponified, the oil is washed to remove the soaps,neutralized and further washed to remove excess chemicals and soaps. Theoil is then bleached to remove color bodies and then finally deodorized.Since an alkali is used to saponify the free fatty acids, the process isknown as alkali or chemical refining.

[0005] The capital cost associated with equipment to practice thesechemical refining steps is very high. For example, centrifuges andfiltering equipment, which can be expensive to maintain, are typicallyused to separate the oil from the washing water. Chemical refining alsoinvolves many steps which are cumbersome and which inherently contributeto oil losses, since each of the refining steps produces a residue whichcarries with it a certain quantity of usable oil, thus decreasing theyield of the refined oil.

[0006] Because of the high cost of equipment, the high operating expenseand the losses of product oil, there has been a desire in recent yearsto practice a process commonly referred to as physical refining. In aphysical refining process, crude oil, which has been subjected toseveral pretreatment processing steps, is brought to an elevatedtemperature (250° C. or more) in a vessel operated under vacuum. Steamis sparged into the oil during treatment. Temperature and retention timeconditions are selected such that the free fatty acids and otherimpurities are volatilized and distilled off. The treated oil is thentypically cooled and given a post bleach to further lighten the color ofthe oil.

[0007] Although physical refining offers the advantage of reducedcapital and operating costs, it still requires the crude oil to besubjected to substantial pretreating steps, including the addition ofchemicals to remove at least some of the impurities in the crude oil.These substantial pretreating steps add to the cost of the physicalrefining process, making the fully refined oil resulting from theprocess nevertheless still economically undesirable for industrialapplications.

[0008] The present invention contemplates a physical refining processthat eliminates the substantial pretreatment steps and results in apartially refmed vegetable oil that is useful in industrialapplications.

SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide an economical processfor refining vegetable oils so that they can be used in industrialapplications.

[0010] It is another object of the invention to provide a process forrefining vegetable oils that limits or eliminates yield losses.

[0011] It is a further object of the invention to provide a process forrefining vegetable oils that eliminates the need for chemicalpretreatment of the crude oil.

[0012] These and other objects and advantages of the invention willbecome apparent to one skilled in the art who has the benefit of thisapplication and the prior art.

[0013] One aspect of the invention is a process for partially refining acrude vegetable oil, such as soybean oil. The crude oil is firstdegummed by allowing the oil to sit for a period of time sufficient toallow phospholipids, free fatty acids and other impurities to settle outof the oil. The oil is separated from the impurities, and heated to afirst temperature while being agitated in order to evaporate excessmoisture from the vegetable oil. Then the oil is allowed to cool to asecond temperature within the range of about 170-180° F. and pressurizedair is introduced into the oil as it is being cooled to aerate the oil.The temperature of the oil is then maintained within the temperaturerange of 170-180° F. and the oil is simultaneously aerated and agitateduntil the partially refined oil achieves a desired viscosity.

[0014] Another aspect of the invention is a process for partiallyrefining a crude vegetable oil wherein an alternative degummingprocedure is employed. The alternative degumming procedure comprisessteam heating the crude vegetable oil to a first temperature of about270-300° F. while agitating the oil. Once the oil reaches the firsttemperature, the heat and agitation are turned off and the oil isallowed to settle into layers, wherein the bottom layer contains asubstantial amount of the phospholipid and free fatty acid impurities.The oil is separated from the impurities and then subjected to the samecooling and temperature maintenance steps previously stated to obtain apartially refined oil having a desired viscosity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] It has now been determined that a partially refined vegetable oilsuitable for use in industrial applications such as in making urethanefoams can be obtained from a physical refining process. It should beunderstood that the refining process of the present invention isperformed on crude oil which has already been extracted from theoil-bearing vegetable matter, and is not applied to the oil-bearingvegetable matter itself. Although the process is applicable to a varietyof crude vegetable oils, its predominant commercial concern is directedto soybean oil and will be particularly discussed with reference to thisoil.

[0016] The crude soybean oil obtained from extraction is put into astorage tank and allowed to settle for a period of time sufficient toallow the fines and other insoluble impurities from the extractionprocess, as well as the hydratable and non-hydratable phospholipids orgums present in the crude oil, to settle to the bottom of the tank. Ingeneral, this settling step takes about 20 days. During this time, thephosphorous content of the crude oil decreases because the gums settleto the bottom of the tank.

[0017] After settling, the crude oil is then pumped into a blowing tank,taking care not to pump off the bottom layer which contains the gums andother impurities.

[0018] The degummed crude oil is then heated in the blowing tank to atemperature sufficient to cause the excess moisture present in the oilto bubble up through the oil to the top of the tank. A sufficientheating temperature is in the range of about 260-270° F., with 270° F.being an optimum temperature. Temperatures above 270° F. tend to causedarkening or scorching of the oil, while temperatures below about 260°F. are not hot enough to efficiently cause the excess moisture to movethrough the oil.

[0019] As the oil is heated it is continuously agitated to promotemovement of the moisture through and out of the oil. The equipment usedto accomplish the heating and agitation of the oil can be any heatingand agitation equipment known to those knowledgeable in soybeanprocessing. For example, it has been found useful in the present processto equip the blowing tank with steam coils positioned near the bottom ofthe tank to accomplish the heating of the oil and to equip the blowingtank with an impeller to accomplish the agitation.

[0020] Once the temperature of the oil in the blowing tank reaches about270° F., the heat and agitation are turned off, and the oil is thenaerated by introducing air under pressure into the blowing tank.Although a variety of aeration equipment could be used to accomplish theaeration step, one useful design is to equip the tank with perforatedpipe that is placed near the bottom of the blowing tank.

[0021] The air is introduced into the oil at a sufficient pressure andat a sufficient rate to cause the air to contact and penetrate all thecrude oil in the tank. An optimum air pressure for the introduced air isabout 120 pounds per square inch and an optimum rate is about 30 cubicfeet per minute.

[0022] It is desirable to have a small amount of moisture present in theoil, such as about 0.03 to 0.05% moisture. During the heating andagitation step, too much moisture can be evaporated from the oil suchthat the moisture content drops below the range of about 0.03-0.05%. Itis then necessary to bring the moisture level up to the optimum range,and this can be accomplished by utilizing humid air in the aerationstep. The amount of humidity is not critical; ambient air at ambienttemperature typically contains sufficient humidity to raise and maintainthe moisture level of the oil at about 0.05%. If additional moisturedoes not need to be added to the oil, i.e. the moisture level is alreadyat about 0.05%, the air can be dried in a dryer prior to beingintroduced into the blowing tank.

[0023] While the oil is being aerated, the heat is turned off and thetemperature of the oil is allowed to drop. When the oil temperaturereaches about 170° F., the amount of air introduced into the oil isincreased to about 130 cubic feet per minute to insure thorough contactand penetration of the air into the oil. The temperature of the oil isthen maintained within the range of 170-180° F. during the remainder ofthe aeration step. In order to maintain a temperature within this range,the heating coils may be turned on as needed to increase thetemperature. Alternatively, if the temperature rises above 180° F.,water can be introduced into the coils to lower the temperature to thedesired range of 170-180° F.

[0024] Although the oil could be maintained at temperatures outside the170-180° F. range, such temperatures are not optimum. At temperaturesbelow 170° F., the viscosity of the oil is higher and the air does notdisperse as well through the oil. If the oil is maintained attemperatures higher than 180° F. there is a danger that the oil willpolymerize and darken in color.

[0025] During the aeration step it is desirable to agitate the oil topromote thorough mixing of the air with the oil. However, care must betaken to make sure that the oil does not reach temperatures over about270° F. because such temperatures can lead to scorching of the oil.Therefore, before air is introduced during the aeration step, theagitator is turned off, since the combination of agitation and aerationcould lead to increases in the temperature of the oil above about 270°F. due to natural friction. As the temperature of the oil drops duringthe aeration step, the agitator can be turned on intermittently toinsure mixing of the air with the oil while minimizing the risk ofincreased temperatures. In general, an agitation time of about 5 minutesevery hour is sufficient. Once the oil temperature drops to about 170°F. the agitation can be constant because the danger of the oil reachingtoo high of a temperature as a result of the frictional forces isminimal.

[0026] Aeration and agitation of the oil are continued until the oilreaches a desired viscosity. In general, the desired viscosity willdepend upon the desired use for the partially refined oil. Viscositiesranging from about 30-40 poise are typical desired viscosities. Once theoil reaches the desired viscosity, the aeration and agitation arestopped and the oil is allowed to cool. The oil tends to polymerize asit is cooling and thereby increase in viscosity. To prevent the oil frompolymerizing, a blanket of nitrogen gas can be introduced into theblowing tank. The oil resulting from the process of the presentinvention has the following characteristics: Free Fatty Acid 3.8 to 2%Moisture 0.05 to .006 Acid Value 1.4 to 3.6 Hydroxyl Value 50 to 125Phosphorus 25 ppm to 110 ppm Gardner Color 5

[0027] The oil resulting from the process of the present invention is alow cost oil suitable for use in industrial applications. Unlike priorart chemical and physical refining processes, the process of the presentinvention avoids the addition of chemicals to refine or pretreat thecrude oil, thereby eliminating expensive equipment such as centrifugesand eliminating additional processing steps.

[0028] In some production situations there may be a demand for thepartially refined oil product that makes it impractical to utilize alengthy settling period such as 20 days. In such situations, analternative degumming procedure can be utilized in the present inventioninstead of using a settling period to remove the gums and otherimpurities.

[0029] In the alternative degumming procedure, the extracted crude oilis pumped directly into the blowing tank. Once in the blowing tank, thecrude oil is heated with live steam introduced through the perforatedpipes. An optimum steam pressure is about 150 p.s.i. The oil is heatedto a temperature that is sufficient to reduce the viscosity of oil suchthat the phospholipids, free fatty acids and other impurities can settleout of the oil. In general a temperature in the range of about 270-300°F. is a sufficient heating temperature, with 300° F. being preferred.Temperatures within this range provide an optimum oil viscosity andtypically do not result in scorching or darkening of the oil because ofthe presence of all the impurities. As the crude oil is heated it iscontinuously agitated to insure thorough mixing of the steam and theoil.

[0030] Once the temperature reaches about 300° F., the heat andagitation are turned off and the oil is allowed to settle in the tank.During settling, the phospholipids, free fatty acids and otherimpurities drop to the bottom of the blowing tank where they can bedrained off. In general, it takes about five hours for the impurities tosettle to the bottom of the tank.

[0031] After the phospholipids, free fatty acids and other impuritiesare drained off, the oil is then subjected to the same aeration stepdiscussed previously in connection with the crude oil that is allowed tosettle for 20 days. Again, the air is introduced at an air pressure ofabout 120 pounds per square inch, and at a rate of about 30 cubic feetper minute. In order to insure that the moisture level in the oil is inthe range of about 0.03-0.05%, it may be necessary to use dried airrather than humid air in the aeration step.

[0032] When the temperature of the oil reaches about 170° F., the amountof air introduced is increased to about 100 cubic feet per minute sothat the air can thoroughly contact and penetrate the oil. Thetemperature of the oil is maintained within the range of 170-180° F. forthe remainder of the aeration step.

[0033] As previously discussed, it is desirable to agitate the oilduring the aeration step. Again, the oil is agitated intermittently asthe temperature is allowed to drop from about 300° F. to a temperaturein the range of 170-180° F., and continuously agitated while the oiltemperature is maintained within the range of 170-180° F.

[0034] Once the oil reaches a desired viscosity, the aeration andagitation are stopped and the oil is allowed to cool. The oil resultingfrom the process employing the alternative degumming procedure has thefollowing characteristics: Free Fatty Acid 2.75 to 2% Moisture .05 to.006 Acid Value 2 to 3.6 Hydroxyl Value 50 to 72 Phosphorus 5 ppm to 15ppm Gardner Color 5

[0035] Utilizing the alternative degumming procedure results in an oilhaving a lower phosphorus content because the steam used in thedegumming procedure draws more phosphorus out of the oil than if the oilis degummed through settling alone.

[0036] Numerous modifications may be made to the foregoing processwithout departing from the basic teachings thereof. Although the presentinvention has been described in substantial detail with reference to oneor more specific embodiments, those of skill in the art will recognizethat changes may be made thereto without departing from the scope andspirit of the invention as set forth in the appended claims.

What is claimed is:
 1. A method of partially refining crude vegetable oil containing gums and other impurities comprising the steps of: (a) permitting the crude vegetable oil to settle over a period of time such that the oil becomes stratified into at least two distinct layers, with one layer comprising gums with a low oil content and a second layer comprising oil containing a fraction of the gums originally present in the oil; (b) separating the oil layer from the gum layer and heating the oil layer to a first temperature which is sufficient to evaporate moisture present in the oil; (c) agitating the oil while it is being heated to said first temperature; (d) allowing the oil to cool to a second temperature within the range of about 170-180° F.; (e) introducing air under pressure into the oil as it is cooling to said second temperature; (f) maintaining the oil within the temperature range of 170-180° F. for a time period sufficient to achieve a desired viscosity; (g) agitating the oil during step (f) and aerating the oil during step (f) with air under pressure; and (h) allowing the oil to cool to ambient temperature without agitation or aeration to obtain a partially refined vegetable oil.
 2. A method in accordance with claim 1 , wherein the first temperature is in the range of about 260-270° F.
 3. A method in accordance with claim 1 therein agitation of the oil is constant as the oil is being heated to said first temperature.
 4. A method in accordance with claim 1 , wherein the air introduced in step (e) is introduced at a pressure of about 120 pounds per square inch.
 5. A method in accordance with claim 4 wherein the air introduced in step (e) is introduced at a rate of about 30 cubic feet per minute.
 6. A method in accordance with claim 1 wherein the oil is intermittently agitated as it is cooling to said second temperature.
 7. A method in accordance with claim 1 wherein the oil is constantly agitated while it is being maintained within the temperature range of 170-180° F.
 8. A method in accordance with claim 1 wherein the air used to aerate the oil during step (f) is at a pressure of about 120 pounds per square inch.
 9. A method in accordance with claim 8 wherein the air used to aerate the oil during step (f) is introduced at a rate of about 130 cubic feet per minute.
 10. A method of partially refining crude vegetable oil containing gums and other impurities comprising the step of: (a) heating the crude vegetable oil to a first temperature of about 300° F.; (b) agitating the vegetable oil while it is being heated to said first temperature; (c) permitting the heated crude vegetable oil to cool and to settle over a period of time such that the oil becomes stratified into at least two distinct layers, with one layer comprising gums with a low oil content and a second layer comprising oil containing a fraction of the gums originally present in the oil; (d) separating the gum layer from the oil layer and allowing the oil to cool to a second temperature within the range of about 170-180° F.; (e) introducing air under pressure into the oil as it is cooling to said second temperature; (f) maintaining the oil within the temperature range of 170-180° F. for a time period sufficient to achieve a desired viscosity; (g) agitating the oil during step (f) and aerating the oil during step (f) with air under pressure; and (h) allowing the oil to cool to ambient temperature without agitation and aeration to obtain a partially refined oil.
 11. A method in accordance with claim 10 wherein the vegetable oil is agitated constantly as it is being heated to said first temperature.
 12. A method in accordance with claim 10 wherein the heating in step (a) is accomplished by introducing steam under pressure into the crude vegetable oil.
 13. A method in accordance with claim 10 , wherein the air introduced in step (e) is introduced at a pressure of about 120 pounds per square inch.
 14. A method in accordance with claim 13 wherein the air introduced in step (e) is introduced at a rate of about 30 cubic feet per minute.
 15. A method in accordance with claim 10 wherein the oil is intermittently agitated as it is cooling to said second temperature.
 16. A method in accordance with claim 10 wherein the oil is constantly agitated while it is being maintained within the temperature range of 170-180° F.
 17. A method in accordance with claim to wherein the air used to aerate the oil during step (f) is introduced at a rate of about 100 cubic feet per minute. 